1. Technical Field
The present invention relates to a heat exchanger including a heat exchanging module which is configured by stacking a plurality of plates each having a groove for allowing fluid to flow, and a pressure vessel for accommodating the heat exchanging module therein.
2. Relevant Art
Conventionally, a PCHE (Printed Circuit Heat Exchanger) type heat exchanger is well known as this type of the heat exchanger as shown, for example, in the following non-patent document 1 and patent document 1.
This type of heat exchanger is configured such that a plurality of plates are stacked and grooves for allowing fluid to flow are formed to portion between the adjacent plates. Two kinds of fluids of which temperatures are different for heat exchanging are flown through the grooves such that one groove is used for flowing one fluid while the other (adjacent) groove is used for the other fluid.
In comparison with a shell-and-tube type heat exchanger or a helical coil type heat exchanger in which two kinds of liquids having temperature difference for heat exchanging are contained in grooves formed between the plates, the PCHE type heat exchanger has characteristics such that a heat exchanging performance is good and a pressure withstanding property is excellent. The structure of this conventional heat exchanger will be explained with reference to the drawings.
FIG. 11 is a cross sectional view showing the conventional heat exchanger, and FIG. 12 is a longitudinal sectional view showing the conventional heat exchanger (a sectional view taken along the line XII-XII of FIG. 11).
As shown in these FIGS. 11 and 12, the PCHE type heat exchanger 1 has a structure in which an outer partition wall 11b and an inner partition wall 11a each having a polygonal shape (for example, hexagonal shape) are provided in a pressure vessel 10, and a plurality of heat exchanging assemblies 9 (for example, six assemblies) are evenly arranged in the inner portion of the inner partition wall 11a in a circumferential direction thereof.
At inner and outer surfaces of the respective heat exchanging assemblies are formed with: a fluid inlet flow path 4a allowing one fluid for heat exchanging (hereinafter, referred to as “fluid A”) to flow in a direction as indicated by an arrow A; and a fluid inlet flow path 4b for allowing the other fluid (hereinafter, referred to as “fluid B”) to flow in a direction as indicated by an arrow B.
At upper portions of the hexagonal-shaped partition walls 11a and 11b constituting the flow paths for a fluid B outlet fluid is attached with a head portion 12 which constitutes a flow path for a fluid B inlet fluid 5a. A fluid A inlet pipe 8a and a fluid A outlet pipe 8b are connected to an upper portion of the head portion 12, respectively.
The heat exchanger uses a heat exchanging module 3 which is formed in a height direction by stacking a plurality of heat exchanging elements formed with the fluid A flow path and the fluid B flow path, and integrating the same by means of welding.
FIGS. 13A to 13D are explanatory views each showing assembling state of the conventional heat exchanging module, and FIGS. 14A to 14F are explanatory views each showing the conventional heat exchanging assembly.
As shown in FIGS. 13A to 13D, the heat exchanging assembly 3 is arranged in two-rows and is mounted with a partition plate 6 for partitioning a space between the fluid A inlet flow path 4a and the fluid A outlet flow path 4b, and a header 7 for partitioning the fluid A outlet flow path 4b from the fluid B inlet flow path 5a, respectively.
Then, as shown in FIGS. 14A to 14F, the header 7 is mounted to upper and lower portions of the heat exchanging assembly 3. The fluid A inlet pipe 8a and the fluid A outlet pipe 8b are connected to the head portion 12 of the upper side, respectively, thereby forming the heat exchanging assembly 9.    [Patent Document 1] Japanese Patent Application, Laid-Open, No. 2006-314864    [Non-Patent Document 1] HEATRICTUM Workshop 2 Oct. 2003, Personal Communication, MIT, Cambridge: MA, 2003
In the heat exchanger configured as described above, due to the heat exchanging operation between the fluid A and the fluid B, the temperature of the fluid B at the fluid outlet reaches to a temperature close to that of the fluid A. Accordingly, a space within the inner partition wall 11a and a space between the outer partition wall 11b and the pressure vessel 10 shown in FIGS. 11 and 12 are heated to exhibit a high temperature. Therefore, for the purpose of securing a soundness of the materials and lowering a heat loss, it is necessary to attach a heat insulating material onto surfaces of the partition walls 11a, 11b and the pressure vessel 10 to thereby lower the temperature.
On the other hand, the heat exchanging assembly 9 is also exposed to a high temperature environment by the heat of the fluid A at the fluid inlet, so that an amount of thermal expansion in a height direction of the heat exchanging assembly 9 becomes large in comparison with that of the pressure vessel 10. In this regard, in a case where the heat exchanging assembly 9 is used under a high temperature and a high pressure conditions, the heat exchanging assembly 9 is manufactured from austenite type stainless steel or nickel based alloy, while the pressure vessel 10 is generally manufactured from carbon steel or chromium-molybdenum steel from viewpoint of economy and lowering the temperature.
In this case, the austenite type stainless steel and nickel base alloy have a relatively large thermal expansion coefficient in comparison with the carbon steel or chromium-molybdenum steel, so that a difference in thermal expansion between the heat exchanging assembly 9 and the pressure vessel 10 becomes greatly large. Therefore, in a case where the outlet/inlet pipes 8a, 8b of the fluid A connected to the upper portion of the heat exchanging assembly 9 are drawn out from the upper portion of the pressure vessel 10 to an outside of the pressure vessel 10, it is necessary to equip and install an expansion joint, for example, bellows type expansion joint for the purpose of absorbing the thermal expansion.
In case of providing this expansion joint, an inverse differential pressure is applied to the expansion joint at the time of loss of fluid A accident. When the differential pressure is large, there may be an extremely high risk of the expansion joint being ruptured, and a fatal damage would occur at a boundary between the fluid A and the fluid B.
Further, in a case where the expansion joint is used under a creep temperature range, an amount of expansion and contraction per one absorbing unit of the expansion joint is limited to an extremely small value so as to prevent a creep fatigue rupture, so that it is required to attach a massive amount of the expansion joints to the pipes. Therefore, a scale and size of the heat exchanger is disadvantageously increased due to installation of the massive joints.
Furthermore, as shown in FIGS. 11 and 12, not only the inner and outer partition walls 11a, 11b, but also supporting plates 13 for supporting the head portion 12 and the heat exchanging assembly 9 are connected to the heat exchanging assembly 9. In general, the heat exchanging assembly 9 is exposed to corrosive fluid and high temperature environment, and is subject to erosion or corrosion by fluids and high-temperature corrosion. Therefore, at a time of periodical inspection or occurrence of damage, a repairing or replacement of members are required. However, since various structural members are combined and connected to the heat exchanging assembly 9 as a main equipment, it is extremely difficult to perform maintenance and replacing operation.